Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Beyond the readOnly/idempotent annotations, the description discloses a paid fee ($0.001 USDC), fail-closed semantics, return of evidence receipt and stable fingerprints, and the critical detail that 'the caller retains sole spending authority.' These behavioral traits are not derivable from annotations alone and significantly aid agent decision-making.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is four sentences with no filler: core identity, usage timing, return payload, and caller authority. The most important facts ($0.001 fee, fail-closed, usage timing) are front-loaded. Every sentence adds distinct value.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a moderation-complex tool with 7 parameters, the description covers cost, failure behavior, output contents, and authority model, while an output schema exists to detail return values. The main completeness gap is parameter semantics, but the invocation context is well specified enough for an agent to proceed.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 0%, so the description must compensate for parameter explanations. It does not explain how to set maxPriceUsd, expectedPayTo, expectedNetwork, allowUnpaidPostProbe, or the body/method relationship, even though some names are somewhat self-explanatory. The only useful tie-in is 'exact observed payment terms,' but this leaves allowUnpaidPostProbe and other fields ambiguous.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a clear purpose: 'Paid $0.001 USDC fail-closed payment authorization preflight' with the explicit usage of verifying before signing an x402 payment. It also specifies return categories (eligible/blocked, terms, reason codes, evidence receipt). It does not explicitly differentiate itself from sibling x402_payment_preflight, which is the only reason it is not a 5.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description gives an explicit when-to-use directive: 'Use immediately before an autonomous agent signs a target x402 payment.' It provides clear context for the tool's invocation but does not mention alternatives, exclusions, or conditions when it should not be used.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.